There arent enough Birds in mono-green for this to be a commander, yet
Interaction Just because this deck loves to attack doesnt mean it ignores what your opponents are doing
With Isshin out in play, if a creature attacks and causes a trigger of a card you control to go off, that trigger happens an extra time
If it's a Siege, it will still be exiled when the last defense counter is removed from it, and its controller may still cast it transformed without paying its mana cost
Its ability to produce mana of any color is valuable, and more importantly, it's a ramp creature that can't be dealt with by conventional removal thanks to hexproof
Ultimates frequently have very splashy abilities that often equate to you win the game. That's the bulk of what you need to know about the rules of planeswalkers and how they work